Total hip arthroplasty is often used to restore function to a diseased or injured hip joint. Positions and directions relative to the hip joint may be described in terms of proximal being nearer the hip joint, distal being further from the hip joint, anterior being nearer the front of the body, posterior being nearer the back of the body, medial being nearer the centerline of the body, and lateral being further from the center line of the body. In total hip arthroplasty, the surfaces of the femur and pelvis are cut away and replaced with substitute implants. In a typical case, the implants include a hip stem component, a femoral head component, an acetabular component, and bone cement.
During preoperative planning, the surgeon typically overlays images of the available implants on an X-ray of the hip joint to determine the appropriate size, offset, and head/neck length to best fit the patient's anatomy and reestablish the anatomic joint mechanics and leg length. During this preoperative planning, the surgeon determines the level for the neck resection that will properly position the implants.
The bone is prepared by first exposing the hip joint by incising and dissecting tissues down to and through the joint capsule. A flat, plate-like, osteotomy guide corresponding to the femoral implant, or at least the neck portion of the implant, is overlaid onto the bone.
The guide includes features for aligning the guide with anatomic landmarks such as the femoral head center, greater trochanter, and/or lesser trochanter. The guide further includes markings indicating the appropriate resection level to properly position the implant. Using the guide as a reference, the surgeon marks the bone at the level of the neck osteotomy with a saw or methylene blue. For example, the guide can have markings indicating the distance up from the lesser trochanter. The surgeon selects the mark that corresponds to his preoperative templating and creates a corresponding mark on the bone. The guide is removed and the neck is cut on the mark to remove the femoral head. The femur is further prepared by reaming and/or broaching the femoral canal down into the bone along an axis from a proximal position near the hip joint at the upper end of the femur toward a distal position nearer the knee joint at the lower end of the femur. The pelvis is prepared by reaming the acetabulum. The implants may be placed directly in contact with the prepared bone surfaces for bony fixation of the implant. Alternatively, bone cement may be introduced into the prepared canal and acetabulum so that it hardens around and locks the components in place.
A recent development is the use of minimally invasive surgical techniques in which the bone is prepared and the implants inserted through small incisions that cause less trauma to surrounding muscles and other soft tissues such that the patient's recovery is faster. Such minimally invasive surgical techniques can be challenging due to the difficulty in visualizing the surgical cavity and maneuvering the instruments and implants within the tight confines of the incision.